Temporal and spatial profiling of the modification of an electroactive polymeric interface using neutron reflectivity

Electropolymerized films of the functionalized pyrrole, pentalluorophenyl-3 -(pyrrol-1-yl)propionate (PFP), were reacted with a solution-phase nucleoph ile, ferrocene ethylamine. This reaction was chosen as a model representati ve of a postdeposition modification of the polymer membrane's properties. F or the first time, a nondestructive method for direct chemical analysis of the reaction profile within the electrodeposited polymer membrane after nuc leophilic substitution is presented. This was achieved through the applicat ion of in situ neutron reflectivity with supplementary analytical informati on concerning the film's chemical composition obtained from XPS, Fr-IR, and electrochemical measurements. The results presented illustrate how, for a partially reacted film resulting from a short reaction time, the extent of reaction with ferrocene ethylamine is not homogeneous throughout the thickn ess of the film, but occurs predominantly at the polymer/solution interface . We show that the progress of the reaction within the polymer film is limi ted by the transport of reacting species in the dense regions of the membra ne that are furthest from the solution interface. The data do not fit an al ternative model in which there is spatially homogeneous progression of the reaction front throughout the bulk of the thin film polymer. Guided by the neutron reflectivity measurements, suitable modifications were made to the electrodeposition method to prepare films whose architecture resulted in fa ster rates of reaction.